Pituitary space-occupying lesions and tumours
Pituitary tumours are the commonest cause of pituitary disease and, as with most endocrine disease, problems may be caused by excess hormone secretion, by local effects of a tumour or inadequate production of hormone by the remaining normal pituitary, hypopituitarism.
Investigation of a possible or proven tumour thus follows three lines:
1 Is there a tumour? How big is it and what local anatomical effects is it exerting? Pituitary and hypothalamic space-occupying lesions, hormonally active or not, can cause symptoms by infiltration of, or pressure on:
• The visual pathways, with field defects and visual loss
• The cavernous sinus, with III, IV and VI cranial nerve lesions
• Bony structures and the meninges surrounding the fossa, with headache
• Hypothalamic centres: altered appetite, obesity, thirst, somnolence/wakefulness or precocious puberty
• Interruption of cerebrospinal fluid (CSF) flow leading to hydrocephalus
• Rarely, invasion of the sphenoid sinus causing CSF rhinorrhoea.
LATERAL SKULL X-RAYS may show enlargement of the fossa. This is a common incidental finding and requires further investigation.
VISUAL FIELDS. These should be plotted formally by automated computer perimetry, Goldmann perimetry and/or by confrontation at the bedside using a small red pin as target. Common defects are upper temporal quadrantanopias and bitemporal hemianopias. Subtle defects may also be revealed by delay or attenuation of visual evoked potentials (VEP).
MRI OF THE PITUITARY, when and where available, is superior to high-resolution CT scanning with reconstruction.
2 Is there a hormonal excess? There are three major conditions that may be caused by tumour or hyperplasia. (a) GH excess, leading to acromegaly or gigantism. These are usually acidophil adenomas. (b) Prolactin excess (prolactinoma or hyperprolactinaemia). Histologically these are chromophobe adenomas; many of these appear to result from an abnormal G protein in the pituitary receptor.
(c) Cushing’s disease and Nelson’s syndrome (excess ACIH secretion)-basophil adenomas or hyperplasia. The clinical features of acromegaly and Cushing’s disease or hyperprolactinaemia are usually, but not always, obvious. Hyperprolactinaemia may be clinically ‘silent’. Tumours producing LH, FSH or ISH are very rare. Some apparently ‘non-functioning’ turnours, which are common and usually chromophobe adenomas, may produce the a-subunit of LH, FSH and ISH.
3 Is there a deficiency of any hormone? Clinical examination may give clues; thus, short stature in a child with a pituitary tumour is likely to be due to GH deficiency. A slow, lethargic adult with pale skin is likely to be ISH and/or ACIH deficient. Milder deficiencies may not be obvious, and require specific testing.
The differential diagnosis of apparent pituitary adenomas additionally includes craniopharyngioma, a usually cystic hypothalamic tumour arising from Rathke’s pouch that often mimicks an intrinsic pituitary lesion. Though presenting at any age, it is the commonest tumour in children and is often calcified.
Less common are cysts of Rathke’s pouch, meningiomas, gliomas, chondromas, pinealomas and carotid artery aneurysms masquerading as turn ours. Secondary deposits occasionally present as apparent pituitary tumours, often presenting as diabetes insipidus.